1. Field of the Invention
The present invention relates to a three-dimensional image processing apparatus capable of obtaining a three-dimensional image from a plurality of images obtained by imaging around a patient, and a reconstruction region specification method in such a three-dimensional image processing apparatus.
2. Description of the Related Art
Three-dimensional (3D) angiography is a technology of generating a fine three-dimensional image of blood vessels such that a plurality of images from different projection views are respectively collected before and after an injection of a contrast medium by repeating imaging while rotating an X-ray tube or the like around a patient, and angiographic blood vessel parts are mainly extracted by subtraction of the collected images before and after an injection of a contrast medium, and the images on which the vessel portions have been extracted are further reconstructed. By an image generated by 3D angiography, it is said to be possible to observe a vessel from an arbitrary angle, and it is particularly useful for carrying out a diagnosis and a medical treatment in a cranial nerve field, in particular, of an aneurysm. An image of an aneurysm generated by 3D angiography has the following clinical usability.
1. It is possible to identify an angle from which it is easy to view an aneurysm.
In order to carry out a diagnosis and a medical treatment of an aneurysm, information from an angle from which it is easy to view a neck of the aneurysm is extremely important. However, because an X-ray image has only two-dimensional information, it is not easy to identify an image from an angle from which it is easy to view a neck of the aneurysm. Until the development of a 3D angiography device, all identification operations have been carried out by trial and error. To describe concretely, it is the procedure in which an observation angle is switched (randomly) to an angle thought fit to observe, and when a neck of an aneurysm cannot be seen, an observation thereof is made from another angle. Identification of an observation angle by such a procedure increases not only an inspection time, but also an exposure dose and an amount of a contrast medium onto a patient, and the like, which increases a burden onto the patient. In contrast thereto, by 3D angiography, it is possible to obtain fine images from all angles around the patient, and thus it is possible to carry out identification of an observation angle of an aneurysm image in a short time as compared with that in the conventional art.
2. It is possible to obtain an image on which it is possible to easily grasp a relationship between a neck and a dome of an aneurysm.
A relationship between a neck and a dome of an aneurysm is extremely important for deciding on courses of treatment. For example, in a case of carrying out a treatment for an aneurysm by coil embolization, when a neck is significantly smaller than a dome, a coil is stabilized in the aneurysm. However, if this is not the case, even when the coil is kept in the aneurysm, the coil deviates into a main blood vessel, which brings about the risk that a peripheral blood vessel is embolized unfortunately. Accordingly, in the latter case, it has been thought that a risk that coil embolization is used for a treatment for an aneurysm is high, and there are many cases in which a surgical treatment (a clipping surgery) is applied thereto. It is easy to make such a judgment in an aneurysm image generated by 3D angiography.
3. It is possible to obtain an image on which it is possible to identify branch connections of capillary blood vessels diverging from the vicinity of an aneurysm.
With respect to a capillary blood vessel diverging from the vicinity of an aneurysm, it is difficult to confirm where the blood vessel diverges from. If the capillary blood vessel diverges from a dome of the aneurysm, the blood vessel itself is embolized by using coil embolization. If the blood vessel serves an important role in brain function, critical damage will be caused. Accordingly, when a capillary blood vessel diverges from a dome of an aneurysm, it is important to know whether the blood vessel diverges from the aneurysm, or diverges from the other blood vessel. Generally, when the blood vessel diverges from the aneurysm, it has been thought that the risk of coil embolization is high, and there are many cases in which a surgical treatment (a clipping surgery) is applied thereto.
Further, on an aneurysm image generated by 3D angiography, it is possible to confirm not only the various information described above, but also an anatomical position. For example, when there is an aneurysm in the vicinity of the base of the brain, it is possible to judge that a surgical approach is difficult.
In order to make a judgment as described above (in particular, the judgment of 2 or 3), precise information is required. A good deal of time is necessary for reconstructing the precise information. However, considering the fact that such information is required in process of intervention in which a diagnosis and a treatment are carried out at substantially the same time, the information is preferably provided in a short time. Generally, an image display within one minute is desired. However, it is difficult to display precise information within one minute even by using a most advanced high-speed arithmetic chip.
Here, as one of the methods for shortening a reconstruction time, there is a technique of limiting a region on which reconstruction is carried out (called ROI). It is assumed that a filtered backprojection method which is general as a reconstruction technique is used. Because a backprojection operation is dominant in a reconstruction time, provided that a voxel size can be limited to be half per one side, one eighth of a usual a reconstruction time is enough. There is hardly any case in which information on an entire blood vessel is required clinically in practice, and for example, in a case of an aneurysm, it suffices to represent the aneurysm, a main blood vessel thereof, and peripheral blood vessels thereof. Thus, the limitation of a reconstruction region is a limitation which is easy to be accepted clinically as well.
As one of the methods for limiting the reconstruction region described above, there is a method in which images of a front face and side faces (separated by 90°) are displayed to be next to one another, and a circular or rectangular reconstruction region is specified by specifying a center and a size in each of the images. However, in such a method, it is necessary to input at least four data (two data×two images) in order to carry out reconstruction. Further, respective target structures of the front face and the side faces are preferably clearly observed. However, there are cases in which it is difficult to judge where a target structure is due to one of those being superimposed on another vessel. In such a case, an image which is in a direction relatively close to the image on which it is difficult to judge a target structure, and which can be clearly judged is selected, and a center and a size are specified in the newly selected image. In this case, further extra operations are required.
However, as described above, 3D angiography is a function required particularly in process of intervention, and an operation requiring many processes as described above is unacceptable.